Where Is Shadeless Material Option For Blender 2.8?
The option shown there is for Blender Internal renderer, which has been removed in Blender 2.8. See the following questions for information on how to create a shadeless material using the shader node graph.

Totally white shadeless material in Cycles?

Node for setting render colour, regardless of lighting

These setups will work for both Cycles and EEVEE in Blender 2.8